1. Field of the Invention
The present invention relates to a regenerative and anti-lock braking system for motor vehicles.
2. The Prior Art
The growing utilization of automobiles greatly adds to the atmospheric presence of various pollutants including greenhouse gases such as carbon dioxide. Accordingly, a need exists for significant improvement in the efficiency of fuel utilization for automotive powertrains.
Braking requires the removal of kinetic energy from a vehicle in motion. Conventional braking systems do this by means of friction, usually by causing brake linings to rub against a drum or rotor at the command of the driver. Kinetic energy is converted to heat and dissipated to the atmosphere, never to be recovered again (up to 35% of the energy used in typical urban driving is lost to friction brakes). Wheel lock-up, and resultant skidding and loss of control, has always been a possibility in rapid braking because the degree of braking is controlled by the skill of the driver, who has little direct knowledge about the degree of braking that would be necessary to cause a skid.
Anti-lock braking systems have recently been developed to prevent wheel lock-up, but these systems are designed for use with the inefficient friction method of braking. Furthermore, they are used only on conventional automobiles that use traditional internal combustion powertrains. These vehicles cannot achieve regenerative braking without the addition of a secondary energy storage and retrieval system, which would add weight and expense to the car. Since braking would then include both regenerative means and friction means, the anti-lock braking system would have to be substantially modified.
Regenerative braking becomes practical if the vehicle utilizes an unconventional powertrain that inherently allows for recovery of vehicle inertia or kinetic energy via the wheels. Electric vehicles that use batteries are one example, in which the prime mover can either be powered by the battery (as a motor) to drive the wheels, or by the wheels (as a generator) to charge the battery. The effectiveness of regenerative braking systems is determined by the ability of the powertrain in question to absorb energy so as to effect an adequate degree of braking. The power uptake capacity of the powertrain, and the energy storage capacity remaining at any given time, are at least two conditions to which a regenerative braking system must be sensitive. Given these and other considerations, it must respond accordingly, delivering sufficient braking power from a combination of available sources until the driver's demand has been met. This determination often requires complex calculations and sophisticated, expensive hardware implementation. Also, most unconventional powertrains under investigation today are not capable of sufficient power uptake to stop a vehicle in panic braking conditions without significant use of friction brakes.
Anti-lock braking in a regenerative braking system is generally considered to be more difficult to achieve than in conventional anti-lock braking systems which involve only friction brakes. The braking effect provided by the regenerative braking circuit would have to be as rapidly and precisely controllable as conventional friction brakes. It is conceptually easiest to begin with friction brakes and then phase-in regenerative braking until the desired degree of braking is provided. If skidding occurs, friction braking could be reduced until skidding stops. However, it is more energy efficient to always begin with regenerative braking and engage friction brakes only if necessary. Furthermore, if the regenerative circuit is powerful enough, all normal braking can be done without engaging the friction brakes, allowing maximum energy recovery. This would mean that reliable anti-lock control would have to be effected through the regenerative circuit, requiring a regenerative braking means that has precise and rapid controllability. Thus, for maximum efficiency as well as practical anti-lock braking, only certain types of regenerative braking circuits and control schemes qualify.
In summary, without regenerative braking there is little chance for recovering the enormous amount of energy lost to braking. Most regenerative braking systems are costly and complex, would require some degree of friction braking, and would make it difficult to provide the safety of anti-lock braking.